[Plugin: Multiple Post Thumbnails] Re-attach thumbnails after changing name of custom post type

@hippkul: the thumbnails are stored as post meta in the format $post_type_$id_thumbnail_id so when the post type changes, the association is “lost”.

So, to fix this you’ll need to update the metadata keys. Easiest way would be to do it directly on the DB if you have a lot of posts. Otherwise, for just a few posts you can do it using the custom fields metabox in the post edit screen.